1. Field of the Invention
The present invention relates to an electrophotographic method and apparatus such as that employed in a photocopy machine, a facsimile machine, a printer, and a multi functional machine capable of recording an image on a sheet of paper or other image recording medium.
2. Discussion of the Background
In a typical electrophotographic apparatus, 5-20% of a toner, or other image forming substance, used in the electrophotographic process remains on a photosensitive medium, such as a photosensitive drum or belt, without being transferred to the recording medium. In order to preserve the purity of subsequent image forming operations, this residual toner must then be removed and recovered by a cleaning device, otherwise the residual toner will make the next copy appear to be "dirty". The residual toner (i.e., the used toner) exhibits different characteristics than the new toner in that the residual toner does not flow as well as a result of being rubbed and deformed by the cleaning device. That is to say, the used toner has attributes that differ from new toner such that the used toner does not share the same flow characteristics as new toner, and thus, does not reliably reproduce images when recycled and handled in the same way as new toner.
Due to this difference in flow characteristics, many conventional devices simply discard the used toner. Certainly, this approach of discarding 5 to 20% of the total toner, rather than recycling the same, is a much less environmentally friendly process than other devices that recycle the used toner.
FIG. 1 shows a device that recycles toner, where the device is discussed in Japanese Granted Utility Model Application No. 62-26762. FIG. 1 shows a charging device 2, developing device 3, transferring device 4, and cleaning device 5 arranged around a photosensitive medium (i.e., drum 1). The cleaning device 5 is connected to the developing device 3 via a conveyance pipe 6 and a toner conveyance screw 7 is arranged to rotate within the conveyance pipe 6 so as to move the used toner therethrough. As a result, the used toner is recycled by being transported from the cleaning device 5 into the developing device 3 by rotation of the toner conveyance screw 7.
FIG. 2 shows another conventional apparatus that recycles toner as discussed in Japanese Granted Patent Application No. 62-36226, which corresponds directly with Japanese laid-open Patent Application No. 55-73078. In the apparatus of FIG. 2, a charging device 102, developing device 103, transferring device 104, and cleaning device 105 are arranged around a photosensitive medium 101. A used toner conveyance pipe 106 is rotatably installed in the developing device 103, as shown. A pipe connector 108 is installed in the cleaning device 105, as shown, such that used toner from the cleaning device 105 passes to the developing device 103 via the conveyance pipe 106 and the pipe connector 108. In this configuration, the conveyance pipe 106 is arranged horizontally, as noted by a solid line, and thus requires a set of rotatable screws 109 which urge the used toner toward the developing device 103. During a maintenance operation that requires the photosensitive medium 101 to be removed, the pipe connector 108 and conveyance pipe 106 rotate out of the way, as is illustrated by the dashed line in FIG. 2. In this configuration, the conveyance pipe 106 is no longer operable, but sufficient clearance is obtained so that sufficient access is made available for servicing the photosensitive medium 101.
As recognized by the present inventors, a limitation with the apparatus described in Japanese Granted Utility Model Application No. 62-26762 (i.e., the device of FIG. 1) is that it requires the use of an activated conveyance pipe 6 with a conveyance screw 7 therein so as to move the used toner to be added directly to the developer, without first being mixed with new toner. The dedicated conveyance path with the active conveyance screw 7 is costly to manufacture and does not necessarily ensure adequate mixing of the used toner with the new toner.
Similarly, in the device described in Japanese laid-open Patent Application No. 55-73078, the used toner conveyance coil 109 is needed to convey the used toner to the developer because the conveyance path is generally horizontal. This dedicated conveyance path with the active conveyance screw 109 is costly to manufacture and is does not necessarily ensure adequate mixing of the used toner with the new toner.